Maltol is a naturally occurring substance found in the bark of young larch trees, pine needles and chicory. Early commercial production was from the destructive distillation of wood. Synthesis of maltol from 3-hydroxy-2-(1 piperidylmethyl)-1,4-pyrone was reported by Spielman and Freifelder in J. Am. Chem. Soc. 69, 2908 (1947). Schenck and Spielman, J. Am. Chem. Soc. 67, 2276 (1945), obtained maltol by alkaline hydrolysis of streptomycin salts. Chawla and McGonigal, J. Org. Chem. 39, 3281 (1974), and Lichtenthaler and Heidel, Angew. Chem. 81, 999 (1969), reported the synthesis of maltol from protected carbohydrate derivatives. Synthesis of gamma-pyrones, such as pyromeconic acid, maltol, ethyl maltol and other 2-substituted-3-hydroxy-gamma-pyrones are described in U.S. Pat. Nos. 3,130,204; 3,133,089; 3,140,239; 3,159,652; 3,365,469; 3,376,317; 3,468,915; 3,440,183 and 3,446,629.
Multi-step syntheses based on furfuryl alcohols and requiring the preparation of intermediate epoxy ketones have been reported by Shono and Matsumura, Tetrahedron Letters No. 17, 1363 (1976), Torii et al., Chemistry Letters, No. 5, 495 (1976) and such a synthesis is described in co-pending U.S. Pat. application Ser. No. 608,452, filed Aug. 28, 1975, assigned to the assignee of the present application. A one-pot process for preparing useful gamma-pyrones from unsubstituted furfuryl alcohols is described in co-pending U.S. Pat. application Ser. No. 710,901, filed Aug. 2, 1976, now abandoned.
Maltol and ethyl maltol enhance the flavor and aroma of a variety of food products. In addition, these materials are used as ingredients in perfumes and essences. The 2-alkenyl-pyromeconic acids reported in U.S. Pat. No. 3,644,635 and the 2-aryl-methylpyromeconic acids described in U.S. Pat. No. 3,365,469 inhibit the growth of bacteria and fungi and are useful as flavor and aroma enhancers in foods and beverages and aroma enhancers in perfumes.